Various techniques have been developed for the preparation of oil-in-water emulsions. One method titling "Emulsification Method" is proposed in U.S. Pat. No. 4,349,455.
Referring to FIG. 1, there is shown a cross section of an apparatus for use in the practice of the method of emulsification as described in U.S. Pat. No. 4,349,455. In a dissolving-emulsifying tank 2 equipped with a high-speed rotor 1, a hydrophobic substance or a mixture of a hydrophobic substance and an emulsifying agent is added directly or after being dissolved in an organic solvent by heating to form a hydrophobic substance solution as an oil phase. Then, into the tank 2 through a conduit 3 is introduced water singly or in combination with an emulsifying agent while stirring to form a water-in-oil emulsion. Addition of water or a mixture of water and the emulsifying agent is continued until the phase inversion occurs, whereupon an oil-in-water emulsion is formed. Thereafter, a water-soluble binder is added to the above prepared oil-in-water emulsion to form the desired oil-in-water emulsion.
The present invention is directed to improvements in the method of emulsification as described above. Thus, it offers various advantages: for example, the dispersion efficiency is improved, the mean particle size is further decreased, the particle size distribution is narrowed and made sharp, and the emulsification can be performed in a short period of time.